Sorptive materials such as desiccants can be supplied in a loose granular form but this can lead to contamination of product with which they come into contact. To overcome this problem, sorptive materials have been supplied as sachets with the particulate sorbent enclosed in a porous material. However, this can lead to clumping of the sorbent in one area of the sachet and consequent inefficient use of the sorbent. To overcome this problem, the sorptive material has been provided as a sachet having multiple discrete connected smaller areas.
Sorptive materials have also been incorporated into polyolefin films, particularly where the sorptive material is used in a multilayer construction to protect a moisture-sensitive layer such as a film of an ethylene/vinyl alcohol copolymer. However, in such constructions the sorptive material absorbs water vapor at appreciable rates only when heated during a retort process.
To overcome such problems, films have been developed wherein the films have a polymeric matrix with a system of interconnecting micropores and are loaded with particulate sorbent material which may be a desiccant material. Such films are produced by forming a melt blend of the sorbent particles, the polymer and a selected diluent, extruding the film and removing the diluent. The water to be sorbed, generally as water vapor, can then rapidly contact the particulate material through the pores of the polymeric matrix, and sorption of the water by the particulate material can be achieved. However, when the sorbent particulate material is thus available for sorption of the water, the film must be carefully stored prior to use to prevent premature sorption of environmental water vapor and should be protected with a dry atmosphere during manufacturing and converting.
In addition to desiccants for sorption of water, there is also need to sorb other materials such as carbon dioxide and acidic gases and a wide variety of organic materials.
U.S. Pat. No. 4,550,123 teaches textile quality polymeric fibers or thin films made porous by extraction of a diluent included during manufacture of the fiber or film. This reference does not contemplate fibers or films in which a wax is retained in the fiber or film during use of the fiber or film. This reference states in column 3, lines 21-27, the yarns, fibers or films so formed, are extracted with a suitable solvent or solvents for removal of the diluent. This extraction porosifies the polymer leaving the sorbent particles in an active state accessible to vapors, liquids or solutes present on or at the surface of the matrix.
U.S. Pat. No. 4,626,252 discloses backing sheets for a diaper which are made from a stretched extruded film made from a polyolefin, a wax like hydrocarbon polymer and a filler. Presumably the particles are included to assist in formation of pores with film when the film is stretched.